In many steelmaking processes, water-cooled steelmaking lances are inserted into a steelmaking furnace vessel (e.g., a basic oxygen furnace (BOF), electric arc furnace (EAF), etc.), to promote melting, decarburization, refining and other processes useful in converting iron-containing scrap material within the vessel into steel. A typical lance may inject gaseous materials such as oxygen, hydrocarbon gas and/or inert gas at high velocity at various times to achieve desired treatment of the scrap metal and/or maintenance of the interior of the vessel. Some lances may also inject particulate carbon and/or lime (or similar substances) to achieve desired properties in the steel ultimately produced.
Water-cooled lances generally comprise an adapter portion, an elongated barrel portion connected at a first end thereof to the adapter portion and lance tip portion connected to a second end of the barrel portion.
The adapter portion comprises at least one inlet for receiving the gaseous and/or particulate matter to be injected into the furnace vessel, which matter will hereinafter be generally referred to as "active material." The adapter portion also includes a water outlet and a water inlet for circulating pressurized cooling water throughout the lance.
The barrel portion comprises at least three substantially concentrically arranged metal, typically steel, pipes for communicating the cooling water and/or active material(s) between the adapter portion and the lance tip portion. The outermost and first innermost pipes normally define an annular water return passageway for conveying coolant water from the lance tip portion to the adapter portion. The first and second innermost pipes normally define an annular water delivery passageway for conveying coolant water to the lance tip portion from the adapter portion. And, the interior of the second innermost pipe (and any additional pipes arranged concentrically interiorly thereof) defines at least one passageway for conveying active material from the adapter portion to the lance tip for injection into the furnace vessel.
The lance tip portion usually comprises an assembly having comprising one or more parts which may be secured by welding, soldering or the like to the concentric pipes of the barrel portion. The lance tip assembly comprises at least one nozzle in communication with the at least one active material passageway of the barrel portion for injecting or discharging the active material into the furnace vessel. The tip assembly further comprises passage means for connecting the water delivery and return passageways of the barrel portion to one another. So constructed, water or other coolant fluid may be continuously circulated through the lance to cool the lance, especially the lance tip assembly which is exposed to the greatest temperatures during lance operation. Indeed, if coolant water is not effectively conveyed through the lance tip portion then the assembly may become non-uniformly heated. This, in turn, may lead to so-called "hot-spots" or "burn-through" sites which often result in premature failure of the lance tip.
A common practice means by which the steelmaking lance manufacturing industry has sought to impart cooling to the lance tip assembly is to provide a generally centrally disposed protrusion or dimple at the inside face of the tip assembly. The object of such protrusion is to direct coolant water radially outwardly through the interior space of the lance tip to cool all areas of the working face of the lance tip. The water-diverting protrusions have assumed an assortment of sizes and shapes and have met with varying degrees of success for their intended purposes. Examples of such protrusions may be found in U.S. Pat. Nos. 3,224,749; 3,525,508; 3,525,509; 3,823,929; 3,827,632; 4,083,539; 4,083,541; 4,083,542; 4,083,543; 4,083,544; 4,106,756; 4,230,033; 4,322,033; 4,432,534; 4,702,462; 4,951,978 and Reissue Pat. No. 28,769. None of these patents appear to suggest any cooling advantages arising from engineering the interior space of the lance tip assembly, including or separate from the aforesaid protrusion, to achieve a substantially uniform cooling of the working face of the lance tip. Moreover, these patents acknowledge cooling benefits that might arise by minimizing the distance between the coolant water as it is circulated across the inside face of the tip assembly and the critical nozzle exit. The phrase "critical nozzle exit", as used herein, shall be construed to mean the radially innermost point of the discharge opening of each nozzle in the lance tip in relation to the geometric center of the lance tip. In contrast, the present inventors have discovered that by minimizing the distance between the coolant water and the critical nozzle exit, relative cold and hot spots are reduced at the working face of the tip, thereby reducing nozzle erosion and burn-through at the outside surface of the tip face.
U.S. Pat. Nos. 4,052,005 and 4,951,928 have acknowledged the desirability of providing elevated coolant water flow velocity at the inside face of the lance. However, the elaborate lance tip constructions disclosed therein are costly and difficult to manufacture and do not assure that optimum water flow velocity and attendant uniform tip cooling can be reliably achieved in lances of varying size. U.S. Pat. No. 4,951,928, for example, provides for radially asymmetrically arranged secondary channels or pipes which are disposed within the coolant water delivery passageway to create a radially asymmetric flow at the center or protrusion region of the lance tip. However, no reference is made to any optimum water flow velocity at the protrusion or any other region of the interior face of the tip or that the secondary channels can achieve uniform velocities and/or cooling capabilities in areas of the working face other than the protrusion.
The prior art also includes lance tip assemblies made from one or more pieces of forged or cast copper. For example, U.S. Pat. No. 4,396,182 discloses a single piece copper casting; U.S. Pat. No. 4,533,124 teaches a one or two piece copper casting; U.S. Pat. No. 4,301,969 provides a one piece forged copper member; U.S. Pat. Nos. 3,662,447 and 4,702,462 describe multipiece forged copper constructions; and U.S. Pat. No. 3,559,974 discloses a multipiece assembly comprising a worked, e.g., forged, copper base portion welded to a cast copper body portion. Of these, U.S. Pat. No. 3,559,974 couples the deterioration resistance afforded by the dense, fine-grained structure of a copper forging at the exposed working face lance tip with the economy of a copper casting at the interior of the lance which is subject to far less heat and caustic conditions than the working face.
The lance tip assembly disclosed in U.S. Pat. No. 3,559,974 also includes worked, e.g., forged, copper exit conduits and nozzles for discharging oxygen into the furnace vessel. The worked discharge nozzles are structural elements distinct from both the cast copper body portion and the worked base portion and require three separate welds per nozzle to secure the nozzle to the body and base portions. The very number of nozzle welds required to join the body and base portions considerably complicates assembly of the lance tip structure and increases the likelihood of weld failure during lance operation.
An advantage exists, therefore, for a combined forged and cast lance tip assembly which is comparatively easy to assemble and durable in operation which further provides substantially uniform cooling of the working face of the lance tip by providing high coolant water flow velocity throughout the tip and optimizing the shape characteristics of the interior space of the tip.